In FeedDemon, a desktop based reader, there is a tool called the Panic button that is triggered when you have a lot of unreads (or that you can trigger manually). It displays the following message:
You have 591 unread articles. This isn't email - you don't have to read everything. Perhaps it's time to hit the panic button and let FeedDemon mark articles as read for you?
Then you can mark all articles older than say 48H or 5 days as read automatically.
As a basic feature you can group feeds and there is a button that let you mark all articles in a group (or a single feed) as read, so for chatty feeds you can just skim the titles and if nothing mandates further reading you can clear it up.
The real trick though for me is to revisit your RSS list regularly, say once a year, and not be afraid to remove or filter feeds that post too many articles. Some big blogs in their niche post several "news" pieces per day.
What was great was Yahoo Pipes, where you could filter, merge and transform feeds into new feeds. So you could grab a feed from a chatty blog and filter it on some keyword for the subniche you are interested in, then do that on several sources and merge all these into one consolidated feed.
That's the problem I intended to solve by 'grouping', as I called it: Don't delete the similar items, but group them together (see my GP comment regarding the functionality).
Also, it might not be as hard as it seems with this data. There would be maybe thousands of records (though you'd want it to scale higher); how many would have the same sets of proper nouns, for example, and not be about the same topic?
Let's say it takes an average of 2.5 seconds to read a feed item subject line, decide whether to read it[0], and nothing else - not opening or reading any articles. In half an hour of concentration you could do that with ~700 feed items - again, without reading one article. Let's call 700 feed items a generous maximum; I doubt many will want to devote 30 minutes of their day only to reviewing feed items.
I end up with far more than 700 and I know I'm not the only one. How can I make it faster?
1. Obviously, the UI must not slow me down in any way.
2. Deduplication
3. Grouping of feed items covering the same topic. There may be dozens of items covering the march last weekend: If I don't want to read about it, I can ignore them en masse. If I do want to read about it, I can select the best looking feed item from the group and ignore the rest.
4. Display summaries instead of articles, at least optionally. If an item interests me, I can read the RSS summary and possibly save reading full articles that don't interest me or for which the summary contains the info I want.
... Is there a reader that does all that? Even if I have to pay for it? And it's still not enough; I doubt I could efficiently process all the items using only above. What else can be done?
[0] Source: I just timed myself doing that with 10 feed items in 26 seconds